Quote: "you said"
Not me, that's an official video from the twitch sessions by Lee the lead dev.
But, yes it would carry over levels because it is a global script.
However, you have two options...
1. You can add as many tracks as you want in the music.lua, you're not limited to just 4, so you just add more tracks in music.lua and then create and edit more of the track scripts, and use different track scripts in different levels.
or
2. You can force it to be local, by adding the music.lua script to an entity. So what you do is make multiple copies of the music script and name them music1.lua, music2.lua and so forth (don't forget to renaim the _main and _init lines to match) with different music in each script and place a different one in each level.
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